Gelatin is commonly used as a binder in photographic light-sensitive materials. Typically, light-sensitive silver halide layers, filter layers, interlayers, antihalation layers, overcoat layers, and backing layers contain gelatin as the main binder.
Photographic materials are generally processed in aqueous processing solutions at various temperatures and pH values. If the photographic material contains gelatin that has not been treated with a crosslinking agent (hardener), such processing results in excessive swelling and poor mechanical strength, which can cause uncontrolled image development and physical damage, respectively. And if the processing solution is maintained at a typical elevated temperature, e.g., 40.degree. C., the gelatin binder can dissolve, causing the layers of the photographic material to disintegrate.
In these photographic materials, gelatin can be hardened with various known compounds to reduce swell, and provide good mechanical strength, and resistance to melting of the layers that contain hardened gelatin. Of the many possible hardeners that are available, the hardeners most frequently used by one or more manufacturers of silver halide photographic materials are aldehydes, active halogen compounds, activated olefins and carboxyl-activating compounds.
These commonly used hardeners, however, have one or more disadvantages, when used in photographic light-sensitive materials. These disadvantages include (1) insufficient hardening, (2) slow hardening during storage (afterhardening), (3) low aqueous solubility, (4) adverse effect on photographic characteristics, such as fog and sensitivity (speed), (5) loss of hardener efficiency caused by interaction with other photographic additives, such as couplers, (6) adverse photographic effects caused by interaction with other photographic additives, such as couplers, and the like.
Aldehydes, especially formaldehyde, are well known, commonly used, and relatively inexpensive hardeners. Typical examples of aldehyde hardeners are described in U.S. Pat. No. 3,232,764. Several problems are encountered when aldehyde hardeners are used. Severe health hazards are a concern with the use of aldehydes as hardeners which causes significant handling difficulties. This is a particularly significant problem for formaldehyde because of its volatility. Also, because of its volatility, it is difficult to control the application level of formaldehyde, which can result in significant hardness variability. Another problem is that significant afterhardening occurs with the use of formaldehyde. Still another problem is that aldehydes can react with couplers, which reduces the effectiveness of both the hardener and the coupler.
Problems associated with volatility can be solved by the use of certain well known and commonly used active halogen hardeners, such as described in U.S. Pat. No. 3,951,940. Frequently used active halogen hardeners include 1,3-dichloro-5-hydroxy-S-triazine (DCHT) and 1-chloro-3,5-dihydroxy-S-triazine (CDHT) and derivatives thereof and mucochloric acid. Although active halogen hardeners are usually not volatile, several other problems can be encountered when they are used. One problem is that significant afterhardening frequently occurs. Another problem is that these hardeners release chloride ion during the hardening process, which can cause deleterious sensitometric effects. Another problem is that these hardeners are easily destroyed by hydrolysis, which makes them difficult to prepare, store, and use.
Problems associated with volatility and afterhardening can be solved by the use of certain carboxyl-activating hardeners, such as formamidinium compounds as described in U.S. Pat. No. 4,673,632, heterocyclic dications as described in U.S. Pat. No. 5,236,822, and carbamoylpyridinium compounds as described in U.S. Pat. No. 4,063,952. However, several problems are encountered when these hardeners are used. One problem is that by-products can adversely affect the physical (e.g., tackiness) and sensitometric (e.g., speed and fog) properties of the photographic elements in which they are used. Also, these by-products are sometimes volatile, foul smelling compounds, which can cause health and odor problems. These problems are often aggravated by the fact that carboxyl-activating hardeners are relatively inefficient so that a relatively large amount of hardener is often required to achieve the desired hardening effect. Carboxyl-activating hardeners undergo rapid hydrolysis and they frequently are hygroscopic. These two properties combine to make these hardeners difficult to prepare, store, and use. Still another problem is that carboxyl-activating hardeners can react with couplers, which reduces the effectiveness of both the hardener and the coupler. One attempted solution to this problem was to use carboxyl-activating hardeners only in combination with 2-equivalent couplers, as described in U.S. Pat. Nos. 4,618,573 and 4,863,841. Another attempted solution to this problem was to limit the carboxyl-activating hardener to only certain zwitterionic dication ethers as described in U.S. Pat. No. 4,877,724. However, these potential solutions severely limit the choice of coupler or hardener and do not eliminate the other problems associated with carboxyl-activating hardeners.
Problems associated with by-products and poor hydrolytic stability can be solved by the use of certain activated olefin hardeners such as described in U.S. Pat. Nos. 3,642,486 and 3,841,872. Also, activated olefin hardeners are usually more efficient than hardeners of other classes. However, several problems are frequently encountered when activated olefins are used as hardeners. One problem is that they frequently cause afterhardening. These problems are particularly severe when certain acryloyl compounds, such as 1,3,5-tris(acryloyl)hexahydro-S-triazine, certain vinylsulfonylacetamido compounds as described in U.S. Pat. No. 4,137,082, or certain heterocyclic vinylsulfones as described in U.S. Pat. No. 4,840,890 are used. One attempted solution to the solubility problem was to use a tertiary amine adduct of a heterocyclic vinylsulfone hardener (as a vinylsulfone precursor) as described in U.S. Pat. No. 4,845,024. However, this results in a tertiary amine by-product that can cause deleterious physical and sensitometric effect. Another attempted solution to the solubility problem was to use a sulfoxyethylsulfone hardener (as a vinylsulfone precursor) as described in U.S. Pat. Nos. 4,338,394 and 4,894,324. However, this results in a release of sulfuric acid, which can cause deleterious sensitometric effects. Another attempted solution to the solubility problem was to use a hardener derived from the reaction of a compound having at least three vinylsulfonyl groups and a compound having at least one group (e.g., carboxyl or sulfo) to increase aqueous solubility and at least one group capable of reacting with the vinylsulfonyl group as described in U.S. Pat. Nos. 4,142,897 and 4,554,247. Other attempted solutions to the solubility problem were to use certain vinylsulfone hardeners that have a sulfophenyl group as described in U.S. Pat. No. 4,897,344, certain vinylsulfonylacetyl compounds as described in JP 5,011,395, certain vinylsulfonylmethylsulfones as described in JP 5,011,396, or certain N,N'-bis(vinylsulfonylmethyl)ureas or N,N'-bis(vinylsulfonylmethyl) thioureas as described in JP 5,053,236. However, these compounds are difficult to prepare and purify and they cause relatively severe afterhardening.
It is therefore desirable to provide a hardener that effectively hardens gelatin, is easily and safely synthesized, purified, and handled, is highly water soluble, causes little afterhardening, and does not cause significant deleterious physical and sensitometric effects. It is toward that end that the present invention is directed.
In the photographic arts, there is an abiding interest in providing new classes of hardener compounds such as provided herein. In view of this interest and in view of the hardening properties of the compounds of this invention, it is believed that this invention represents a substantial contribution to the art.
The hardeners of the present invention are characterized by their rapid hardening effects, high aqueous solubility, high aqueous stability, lack of hygroscopicity, lack of deleterious by-products, and/or a lack of deleterious interaction with other photographically useful substances.